1. Field of the Invention:
The present invention relates to a color misregistration easing system for easing color misregistration derived from field sequential imaging.
2. Description of the Related Art:
An endoscope whose elongated insertion tube is inserted into a living body to observe a lesion or other subject has been widely adopted in recent years.
An electronic endoscope system employing a CCD or other solid state imaging device as an imaging means has recently come into practical use.
The electronic endoscope includes a field-sequential type electronic endoscope. Herein, a subject is illuminated with illumination light or red, green, and blue rays having different wavelengths, and imaged under the illumination light. Then, produced images or component images are synthesized to form a single color image.
In this method, component images produced at different times are synthesized to form a single color image. When a moving subject is imaged or an imaging means and a subject are moving relate to one another, a synthetic color image usually has colors different from the original color of the subject.
During endoscopic examination, a mucosa may adhere to an objective at the tip of an endoscope. This hinders accurate observation of images. In this case, water supply is performed; water is injected from the distal end of the endoscope toward the objective in order to clean the lens. During the supply of water, water runs fiercely in front of the objective. When the water is illuminated with field sequential illumination light, the water image is produced with greatly-changed colors or to rainbow-colored. Some endoscopes supply water to wash and cool a subject lesion. FIG. 33 shows the process of color misregistration.
The principles of causing such a color reproduction error will be described in conjunction with FIG. 33. When water is supplied from the distal end of an endoscope, water runs quickly in front of an objective. Then, with red (R) illumination light, for example, the water appears as red water (object) just coming out of the distal end of the endoscope. With green (G) light, a waterdrop moving on the lens surface is visualized as a green object. With blue (B) light, a blue water image is seen having moved farther. On the monitor, a synthetic image of these color images is displayed.
Therefore, a water image is displayed as a primary color image of red, green, blue, yellow, cyan, and magenta with a high saturation. That is to say, the water image is rainbow-colored, causing a doctor to suffer fatigued eyes. This drawback or a color reproduction error attributable to different sampling times of color information is referred to as color misregistration.
In an effort to overcome the drawback, the present applicant has proposed prior art in Japanese Patent Application No. 2-70644. Herein, color component signals are checked to identify color misregistration. Then, when color misregistration is identified, false color signals are supplied together with a real luminance to ease the color misregistration.
In Japanese Patent Application No. 2-27842 (U.S. Pat. No. 5,032,913), the applicant has proposed installation of a water supply detecting means that uses an image signal from an electronic endoscope to identify color misregistration due to water supply. Only when color misregistration derive from water supply is identified, a false color is output. Thus, only intense color misregistration is eased.
Japanese Patent Laid-Open No. 3-24513 has disclosed a color misregistration detector for a field-sequential color misregistration easing system. Herein, a current image is used to generate color difference signals, then the hue is calculated. After that, the hue component is held.
A region with water supplied or another region causing conspicuous color misregistration has a high saturation. In a general image, bleeding appears with a relatively high saturation.
In such a color misregistration detecting method, only a hue component, is used to detect color misregistration. Color misregistration is detected irrelative to the degree. Even negligible color misregistration not usually discerned by an observer is corrected. Color misregistration is detected at a level inconsistent with a level at which a sensory test has revealed that an observer discerns color misregistration. Even indiscernible color misregistration is corrected, deteriorating the quality of observation images.
When color misregistration is detected, color misregistration correction has typically been applied to an entire screen. However, during, for example, the water supply operation or the suction operation, significant color misregistration occurs in part of a screen but color misregistration in the other part is often indiscernible. That is to say, since color misregistration correction is uniformly performed over an entire screen, correction Is applied to portions that need not be corrected. As a result, the corrected image appears unnatural.